1. Field of the Invention
This invention relates to an apparatus for rapidly determining the distribution of radiation doses in the deeper parts of a body which will be helpful when an optimum operating condition is sought for a cancer therapy machine radiating corpuscular beams such as electron beams, or X-rays onto a lesion, and to a detector for detecting such corpuscular beams.
2. Description of the Related Arts
FIG. 14 is a diagram illustrating a conventional deep dose radiation measuring apparatus which determines the distribution of radiation doses in the deeper parts of a body. The conventional radiation deep dose measuring apparatus consists of an ionization box 102 placed in a water phantom 107, and the measurement is achieved with the ionization box 102 which measures the ionization level at a point and converts it into an absorbed amount of radiation. The ionization box 102 is driven, as shown by arrows in the same figure, in the direction of depth (upward or downward) or in a direction (anteroposterior or lateral directions) normal to the axis of corpuscular beams 101 in the water phantom 107, with a driving apparatus 104 and a control system 105. The dose-at-depth measuring apparatus determines the distribution of radiation doses in the water phantom 107.
The conventional radiation deep dose measuring apparatus has a constitution as described above, and its use consists of following procedures: a corpuscular beam 101 ionizes air in the ionization box 102 placed within the water phantom 107, the amount of ionization is amplified with an amplifier 103 for quantification, and the measurement is displayed on a displaying apparatus 106 to represent the distribution of radiation doses. To determine the distribution of radiation doses in the water phantom, the ionization box 102 is moved along X, Y, and Z-axes of a coordinate system assumed in the water phantom 107, and each time the ionization box is moved along one axis, the ionization in the ionization box 102 is determined.
For the conventional radiation deep dose measuring apparatus with such constitution to determine the distribution of radiation doses at depth, it is necessary to move the ionization box 102 placed within the water phantom 107 whenever measurement is undertaken, and thus the measurement with this apparatus requires much time and energy.
Further, to get the distribution of radiation doses in a three dimensional (3D) space, it is necessary to move the ionization box along the three coordinate axes including X-, Y-, and Z-axes one after another, which requires enormous time and energy, too.
Furthermore, if, during measurement, the output of corpuscular beams such as electron beams, or X-rays, (not illustrated here) undergoes fluctuations, the measurement must be renewed to obtain a reliable result of the distribution of radiation deep dose, which also requires much energy and troubles.
Still further, if the ionization box 102 is enlarged to shorten the time necessary for the measurement of doses at depth, the measurement range of one stroke of measurement will be enlarged, but the measurement will be impaired in precision, and the dose measurement along each of the coordinate axes of the water phantom 107 will be reduced in resolution, which will hamper the exact determination of the distribution of doses at depth.
This invention is proposed as a remedy for those problems described above, and intends to provide a radiation deep dose measuring apparatus with a detector measuring radiation doses in a wide range at one stroke with a high resolution which will make it possible to determine the distribution of radiation doses at depth rapidly and with a high precision by moving the detector.